In recent years, developments for renewable energy have been in progress as a countermeasure against global warming. For example, practical use of floating type off-shore wind power generators that transmit electricity from wind power generators, which are ocean floating installations, has been in progress.
To transmit electricity from ocean floating installations, undersea cables are used. An undersea cable includes three power cables that are assembled and twisted together for three-phase alternating current power transmission and armoring wires provided on the periphery of the core to support the cable load.
Since such undersea cables are laid under the sea, high impermeability is required for the internal power cables. Therefore, an impermeable layer is formed on the periphery of the insulator (shielding layer) in the power cables.
On the other hand, such undersea cables are suspended from ocean floating installations that repeatedly oscillate on the sea. Therefore, the undersea cables always deform repeatedly due to fluid force and oscillation of the floating body caused by waves and tides. Therefore, deformation is also repeatedly given to the power cables.
However, it is difficult for the power cables to follow this repetitive deformation if the impermeability thereof is to be formed by a metal layer such as a metal tape. Therefore, it is likely that the metal layer forming the impermeable layer may be damaged, and it is said that fatigue life of the conventional impermeable layer structure is approximately five to seven years, depending on the conditions of the ocean climate.
As such undersea cables, for example, disclosed is an undersea cable including an impermeable layer formed of a multilayer tape in which a metal layer is interposed by resin and the cross sectional shape of the metal layer of the multilayer tape has alternating protrusion and recess shapes formed continuously and repeatedly thereon (Patent Document 1).